High density fiber optic cable

ABSTRACT

A fiber optic cable includes at least one at least one bundle having a plurality of non-tight buffered optical fibers and a binder element for maintaining the integrity of the bundle. The binder element may be, for example, a binder thread. The fiber optic cable may exclude a grease or a grease-like composition being in contact with the at least one bundle for filling interstices of the cable thereby blocking water from flowing through the cable. The fiber optic cable also includes a separation layer for inhibiting adhesion between the bundles of optical fibers and the cable jacket. In another embodiment, a fiber optic cable includes a plurality of optical fibers and a binder element forming at least one bundle. The at least one bundle is surrounded by an armor layer and the fiber optic cable excludes a cable jacket within the armor layer.

RELATED APPLICATIONS

The present application is a Continuation of U.S. Ser. No. 10/005,325filed on Nov. 12, 2001 now U.S. Pat. No. 6,901,191, which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to fiber optic cables and, moreparticularly, to high density fiber optic cables.

BACKGROUND OF THE INVENTION

In many applications, it is desirable for a fiber optic cable to includea plurality of optical fibers. With the increased demand for opticalcommunications, there has been a corresponding demand to increase thenumber of optical fibers, i.e., the fiber count, of a fiber optic cable.By increasing the fiber count of a fiber optic cable, a single fiberoptic cable would be able to support additional optical communicationschannels.

In order to increase the fiber count of fiber optic cables, unitizedfiber optic cables have been developed. As shown in FIG. 1, a unitizedfiber optic cable 10 includes a number of bundles 12 of optical fibers14 that are stranded about a common central strength member 16. Aunitized fiber optic cable 10 also includes a cable jacket 18 extrudedabout the bundles 12 of optical fibers 14, and an optional ripcord 22for facilitating removal of cable jacket 18. As shown in FIG. 1, eachbundle 12 of optical fibers 14 includes at least two and, more commonly,six or twelve optical fibers that are stranded together.

Optical fibers 14 are typically tight buffered optical fibers. A tightbuffered optical fiber 14 includes a single mode or multi-mode opticalfiber that may be surrounded by an interfacial layer. The interfaciallayer can be formed of a Teflon® containing material and is surroundedby a tight buffer layer; however, other suitable interfacial layers maybe used, for example, an UV acrylate. The tight buffer layer istypically formed of a plastic, such as polyvinyl chloride (PVC). As analternative to PVC, the tight buffer layer can be formed of anon-halogenated polyolefin, such as a polyethylene or a polypropylene.Still further, the tight buffer layer can be formed of EVA, nylon orpolyester.

Each bundle 12 of optical fibers 14 also includes a central strengthmember 26 about which the plurality of tight buffered optical fibers isstranded. Each bundle 12 of optical fibers 14 further includes a jacket28 that surrounds the plurality of optical fibers, and an optionalripcord 20 for facilitating removal of jacket 28. Jacket 28 serves toprotect optical fibers 14 and to maintain the bundle of optical fibersin a stranded relationship about central strength member 26. Jacket 28is typically formed of a polymer, such as PVC. As an alternative to PVC,jacket 28 may be formed of a fluoro-plastic, such as polyvinylidenefluoride (PVDF), a fluoro-compound as disclosed by U.S. Pat. No.4,963,609 or blends of PVC and PVDF or PVC and polyethylene (PE). Jacket28 is typically relatively thick and, in one embodiment, has a thicknessof about 0.8 millimeters.

During fabrication, a bundle 12 of optical fibers 14 is passed throughan extruder cross head and jacket 28 is extruded thereabout in order tomaintain the optical fibers in position within the bundle. Since thetight buffer layer of the tight buffered optical fibers 14 is typicallyformed of a plastic, the plastic that is extruded to form jacket 28 willtend to adhere to the tight buffer layer of the tight buffered opticalfibers 14 in the absence of a barrier therebetween. In this regard, theplastic that is extruded to form jacket 28 of a bundle 12 of opticalfibers 14 may partially melt the outermost portion of the tight bufferlayer of the tight buffered optical fibers 14 such that jacket 28 andthe tight buffered optical fibers will adhere to one another as theplastic cools. Unfortunately, the adherence of the tight bufferedoptical fibers 14 to the surrounding jacket 28 generally decreases theperformance of the optical fibers. In this regard, signals propagatingalong optical fibers 14 generally experience greater attenuation asfiber optic cable 10 is bent or flexed in instances in which the tightbuffered optical fibers are adhered to jacket 28 since the opticalfibers will no longer be free to move relative to jacket 28 in order toaccommodate bending or flexure of fiber optic cable 10.

Each bundle 12 of optical fibers 14 therefore also generally includes abarrier 30 disposed between the plurality of tight buffered opticalfibers and jacket 28 in order to separate the tight buffered opticalfibers from jacket 28 and to prevent adherence therebetween thatotherwise would result from the extension of jacket 28 about opticalfibers 14. As such, optical fibers 14 can move somewhat relative tojacket 28 as fiber optic cable 10 is flexed. Barrier 30 is typicallyformed of a layer of strength members, such as aramid yarn, that aretypically stranded about the optical fibers. The layer of strengthmembers is also generally relatively thick and may have a thickness ofabout 0.2 mm in one embodiment.

Each bundle 12 of optical fibers 14 is typically stranded about commoncentral strength member 16 of fiber optic cable 10. Like centralstrength member 26 of each bundle 12 of optical fibers 14, centralstrength member 16 of fiber optic cable 10 is typically formed of arelatively stiff fiber or glass reinforced plastic, or a relativelyflexible combination of aramid fiber that may or may not be overcoatedwith a plastic material. Fiber optic cable 10 also includes a protectivecable jacket 18 that surrounds each of the bundles 12 of optical fibers14. Cable jacket 18 is typically formed of a plastic, such as PVC. As analternative to PVC, cable jacket 18 may be formed of a fluoro-plastic,such as PVDF, a fluoride-compound or blends of PVC and PVDF or PVC andPE.

As described above in conjunction with jacket 28 that surrounds eachbundle 12 of optical fibers 14, cable jacket 18 is also typicallyextruded over the plurality of bundles of optical fibers. As a result ofthe plastic materials that form cable jacket 18 and the jackets 28 thatsurround the respective bundles 12 of optical fibers 14, cable jacket 18and the jackets that surround the respective bundles of optical fibersmay also adhere to one another following the extrusion of cable jacket18 about the bundles of optical fibers. While the adherence of cablejacket 18 to the jackets 28 of the respective bundles 12 of opticalfibers 14 does not impair the performance of fiber optic cable 10 assignificantly as adherence between jacket 28 of a bundle 12 of opticalfibers 14 and the tight buffer layer of the tight buffered opticalfibers, the adherence of cable jacket 18 and the jackets of therespective bundles of optical fibers does disadvantageously impair theflexibility of fiber optic cable 10 somewhat.

Accordingly, fiber optic cable 10 can also include a surface coating onat least that portion of the exterior surface of jacket 28 of eachbundle 12 of optical fibers 14 that otherwise would be in contact withcable jacket 18. The surface coating is typically formed of powderedtalc that serves to prevent or reduce adhesion between cable jacket 18and the jackets 28 of the respective bundles 12 of optical fibers 14.

Unitized fiber optic cable 10 as depicted in FIG. 1 is generallyrelatively large. For example, unitized fiber optic cable 10 depicted inFIG. 1 having six bundles 12 of optical fibers 14 stranded about acentral strength member 16 with each bundle of optical fibers having sixtight buffered optical fibers stranded about a respective strengthmember 26 generally has a diameter of about 18.8 millimeters. In manyapplications, it is desirable to minimize the size of fiber optic cable10 while maintaining or increasing the number of optical fibers 14within fiber optic cable 10. As such, it would be advantageous todevelop a unitized fiber optic cable having a relatively high fibercount while also being somewhat smaller.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed to a fiber optic cableincluding at least one bundle having a plurality of non-tight bufferedoptical fibers and a binder element. The binder element maintains theplurality of non-tight buffered optical fibers in the at least onebundle. A separation layer generally surrounds the at least one bundle,and a cable jacket surrounds the separation layer inhibiting adhesionbetween the at least one bundle and the cable jacket without surroundingeach bundle of optical fibers with a respective jacket. The fiber opticcable excludes a grease or a grease-like composition being in contactwith the at least one bundle for filling interstices of the cablethereby blocking water from flowing through the cable.

Another aspect of the present invention is directed to a fiber opticcable including at least one bundle having a plurality of non-tightbuffered optical fibers and at least one binder thread encircling theplurality of optical fibers to thereby maintain the plurality of opticalfibers in the bundle. A separation layer surrounds the at least onebundle, and a cable jacket surrounds the separation layer inhibitingadhesion between the at least one bundle and the cable jacket withoutsurrounding each bundle of optical fibers with a respective jacket. Thefiber optic cable excludes a grease or a grease-like composition beingin contact with the at least one bundle for filling interstices of thecable thereby blocking water from flowing through the cable.

A further aspect of the present invention is directed to a fiber opticcable including a central member and at least one bundle. The at leastone bundle includes a plurality of non-tight buffered optical fibers anda binder element. The binder element maintains the plurality ofnon-tight buffered optical fibers in the at least one bundle and a cablejacket surrounds the at least one bundle. A separation layer inhibitsadhesion between the at least one bundle and the cable jacket. The fiberoptic cable excludes a grease or a grease-like composition being incontact with the at least one bundle for filling interstices of thecable thereby blocking water from flowing through the cable.

A still further aspect of the present invention is directed to a fiberoptic cable including at least one bundle having a plurality of opticalfibers and a binder element. The binder element maintains the pluralityof optical fibers in the at least one bundle. An armor layer surroundsthe at least one bundle. The fiber optic cable excludes a cable jacketwithin the armor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a cross-sectional view of a conventional fiber optic cablehaving a unitized design according to the prior art;

FIG. 2 is fragmentary perspective view of an exemplary fiber optic cableaccording to one embodiment of the present invention;

FIG. 3 is a cross-sectional view of the fiber optic cable of FIG. 2;

FIG. 2A is fragmentary perspective view of one bundle of optical fibersof the fiber optic cable of FIG. 2;

FIG. 4 is a fragmentary perspective view of an exemplary fiber opticcable according to another embodiment of the present invention;

FIG. 5 is a cross-sectional view of an exemplary tube-assembly of afiber optic cable according to another embodiment of the presentinvention;

FIG. 6 is a cross-sectional view of an exemplary fiber optic cableaccording to another embodiment of the present invention;

FIG. 7 is a cross-sectional view of an exemplary fiber optic cableaccording to another embodiment of the present invention; and

FIG. 8 is a fragmentary perspective view of an exemplary fiber opticcable according to another embodiment of present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring now to FIGS. 2 and 3, a fiber optic cable 40 according to oneembodiment of the present invention is illustrated. Fiber optic cable 40of the present invention can have other configurations as describedbelow, although the fiber optic cable of FIG. 2 will be described inmore detail hereinbelow for purposes of illustration. Fiber optic cable40 includes at least one bundle 42 having optical fibers 44 that arenon-tight buffered; however, optical fibers 44 may be tight-buffered orzipped together. Optical fibers 44 may include, for example, aconventional single mode or multi-mode optical fibers; however, othersuitable optical waveguides may be used. Strength members 46 such as anaramid yarns may be disposed around bundle 42; however, in otherembodiments a plurality of bundles 42 may be disposed around strengthmember(s) 46 disposed in the center of cable 40. More particularly,strength members 46 include a plurality of aramid yarns stranded aroundtwo layers of bundles 42; however, other suitable strength members maybe used, for example, fiberglass yarns. Other embodiments of the presentinvention may include other suitable layers of bundles 42, bundles 42within the same cable having different numbers of optical fibers 44,and/or different types of optical waveguides in the same cable. Fiberoptic cable 40 also includes a cable jacket 50 that surrounds bundles 42of optical fibers 44, and an optional ripcord 54 for facilitatingremoval of cable jacket 50. Additionally, strength members 46 provides aseparation layer between optical fibers 44 of bundles 42 and cablejacket 50 inhibiting the extruded cable jacket 50 from sticking tooptical fibers 44 and/or bundles 42.

Fiber optic cables of the present invention are of a dry cable design.In other words, bundles 42 of the present invention exclude a grease, ora grease-like composition in contact therewith for filling intersticesof the cable thereby blocking water from flowing through interstices ofthe cable. However, fiber optic cables of the present invention mayinclude lubricants allowing bundles 42 and/or optical fibers 44 to moverelative to each other, for example, during bending to improve opticalperformance. Grease compositions are among other things messy andsusceptible to dripping at high temperatures. Moreover, craftsman mustclean the grease from the optical fibers before working with the opticalfibers which is a time consuming process. On the other hand, dry cablesof the present invention allow the craftsman to work with the opticalfibers without first cleaning the grease or grease-like compositionsfrom the optical fibers.

Fiber optic cable 40 of FIGS. 2 and 3 has twelve bundles 42 of twelveoptical fibers 44 for a 144-fiber count cable having a relatively smalldiameter. Each bundle 42 may contain twelve different colored opticalfibers 44 aiding identification of the optical fibers 44 of each bundle42 by the craftsman. Optical fibers 44 are non-stranded, but may bestranded. Bundles 42 of the embodiment are arranged in a first layerhaving three bundles helically stranded, a second layer having ninebundles counter-helically stranded around the first layer and strengthmembers 46 helically stranded around the second layer. In otherembodiments, the first layer of bundles 42 may be stranded around acentral member that may be a strength member, for example, aramid yarns,a glass reinforced plastic, or fiberglass yarns. In still anotherembodiment, a filler rod or other suitable filler member may be usedrather than a bundle 42 of optical waveguides to form fiber optic cable40.

However, the concepts of the present invention may include any suitablenumber of bundles having any suitable number of optical waveguides. Forexample, fiber optic cable 40 may be configured as: a single layer ofthree bundles having twelve optical fibers for a 36 optical fiber countcable; a 72 optical fiber count cable having a single layer of sixbundles stranded around a strength member; an eight-fiber countinterconnect cable; or a 288 optical fiber count cable. The concepts ofthe present invention may also be practiced with other suitable cableconstructions, for example, S-Z stranding or planetary stranding ofbundles 42.

Bundles 42 of fiber optic cable 40 include a plurality of non-tightbuffered optical fibers 44 allowing direct optical fiber to opticalfiber contact among optical fibers 44 and/or bundles 42. However, otherembodiments of the present invention may include tight buffered opticalfibers 44. By eliminating the tight-buffered layer around optical fiber44, the cable diameter may be advantageously reduced allowing for arelatively high fiber density. For example, in one embodiment a 144optical fiber count cable has a diameter of about 10 mm or less.Embodiments including optical fibers 44 with a tight buffer layergenerally increase the cable diameter with a corresponding decrease inthe optical fiber density. For example, in one embodiment a 144 opticalfiber count cable having tight buffered optical fibers 44 has a diameterof about 20 mm or less, whereas a conventional unitized cableconstruction has a diameter of about 30 mm.

Embodiments that include tight buffered optical fibers 44 may besurrounded by an interfacial layer. The interfacial layer is generallyformed of a Teflon® containing material. The interfacial layer thereforeserves as a release layer that provides a controlled bond between thetight buffer layer and the optical fiber so that a craftsman can easilystrip the tight buffer layer from the optical fiber during a terminationprocedure. The tight buffer layer is typically a plastic such as PVC.However, the tight buffer layer can be formed of other plasticsincluding non-halogenated polyolefins, such as PE or polypropylene, afluoro-plastic such as PVDF or an ultraviolet (UV) light curablematerial. Although not necessary for the practice of the presentinvention, the tight buffer layer can also be designed to be flameresistant and to have a riser, a plenum and/or a low smoke zero halogenrating as described by U.S. Pat. No. 6,167,178, the subject matter ofwhich is incorporated herein by reference. For example, the tight bufferlayer of the tight buffered optical fibers can include aluminumtrihydrate, antimony trioxide or other additives to improve the flameresistance of the tight buffer layer.

Each bundle 42 of optical fibers 44 also includes a binder element 48that encircles the optical fibers to maintain optical fibers 44 in thebundle. In one embodiment depicted in FIGS. 2 and 2A, at least onebinder thread 48 encircles the optical fibers 44. Fiber optic cable 40can include various binder threads 48 or binder yarns. Binder thread 48is preferably an air-entangled, textured, continuous multi-filamentthread. In addition, binder thread 48 may be a synthetic thread that isresistant or impervious to bacterial decomposition that would otherwisecreate hydrogen which, in turn, may cause undesirable increases in theattenuation of the signals transmitted via optical fibers 44. By way ofexample, binder thread 48 may be formed of polyester, rayon, nylon orthe like. Moreover, binder thread 48 is preferably pre-shrunk.

Binder thread 48 advantageously has a large spread factor and thereforeflattens once the binder thread is wrapped about optical fibers 44.Additionally, binder thread 48 may readily deform when subjected toadditional forces, such as the forces created by bending fiber opticcable 40. Binder thread 48 typically has no more than about 25 twistsper inch in order to avoid undesirable attenuation of the signalstransmitted via optical fibers 44. Most commonly, binder thread 48 hasbetween about 2 twists per inch and about 6 twists per inch and, morepreferably, about 4 twists per inch. Binder thread 48 also preferablyhas a TEX number between about 18 and about 60 and, more preferably,between about 30 and about 40 such as about 35 in one embodiment suchthat the binder thread has a fluffy feel. Additionally, binder thread 48advantageously has a denier between about 150 and about 2600 such asabout 250 in one embodiment.

Binder thread 48 also preferably includes a finish that is inert withrespect to the components of fiber optic cable 40 with which the binderthread will come into contact. In this regard, the finish of binderthread 48 is preferably inert with respect to the embodiments havingtight buffered optical fibers 44, cable jacket 50 and other suitablecable components and/or materials. For example, binder thread 48 of oneadvantageous embodiment includes a silicone wax emulsion finish thatfacilitates processing of the binder thread. Binder thread 48 may alsobe designed to be non-wicking and/or can include a super-absorbentpolymer in order to reduce or prevent water migration through fiberoptic cable 40.

Binder thread 48 is typically stranded about a respective bundle 42 ofoptical fibers 44 in a helical manner with a pitch of between 10 mm and70 mm and, more preferably, about 50 mm to facilitate fabrication of thebundle of the optical fibers. As illustrated in more detail in FIG. 2A,binder thread 48 of one advantageous embodiment includes a pair ofthreads, namely, a looper thread and a needle thread. As illustrated,one thread, which could be either the looper thread or the needlethread, alternately passes back and forth over the upper portion ofbundle 42, while the other thread alternately passes back and forthunder the lower portion of the bundle. With reference to the embodimentof FIG. 2A, and for purposes of example, the leftmost thread at the endof the bundle that is illustrated extends lengthwise along the bundle toa first stitch at which point the threads are secured by means of anoverlooked stitch. The thread then helically encircles the lower portionof the bundle to a second overlooked stitch on the far side of theillustrated bundle at which point the threads are again secured to oneanother. The thread then extends lengthwise along the far side of thebundle to a third overlooked stitch before again helically encirclingthe lower portion of the bundle to a fourth overlooked stitch. Thispattern is repeated for each thread along the length of the bundle inorder to secure optical fibers 44 together in an integral manner. Inthis embodiment, the looper thread and the needle thread are typicallysecured to one another at a plurality of stitch locations along thelength of the bundle of optical fibers, typically at a pitch of 10 mm to70 mm and, more preferably, at a pitch of 50 mm, by means of anoverlooked stitch. The resulting binder thread has a zig-zag appearanceand is therefore sometimes termed a zig-zag binder.

Further, binder thread 48 can include indicia, such as an identificationmarking or a color, in order to identify the respective bundle ofoptical fibers encircled by the binder thread and to distinguish onebundle from another. For example, one white binder thread 48 may be usedwith a set of twelve different colored binder threads 48 identifyingtwelve bundles 42; however, two sets of twelve different colored binderthreads 48 may be used to identify a plurality of bundles 42.

Binder thread 48 securely maintains the plurality of optical fibers 44within bundle 42, while also maintaining the shape and size of thebundle of optical fibers such that the optical fibers need not bedisposed within a respective jacket or buffer tube as required byconventional fiber optic cables. By eliminating the jacket or buffertube in which a bundle of optical fibers were traditionally disposed,the resulting bundle of optical fibers and, in turn, fiber optic cable40, can be reduced in size relative to a conventional fiber optic cablehaving the same number of optical fibers. Moreover, binder thread 48inhibits optical fibers 44 from being entangled with, for example,aramid fibers.

While a binder thread, such as those described above are advantageousfor maintaining optical fibers 44 in a bundle 42, each bundle of opticalfibers can include other types of binders, if so desired. For example,binder element 48 may be formed of a tape or a film, such as a polymerfilm, that is wrapped about optical fibers 44 as depicted in FIG. 4. Incontrast to the polymer jackets that surround the individual bundles ofoptical fibers of conventional unitized fiber optic cables, the polymerfilm is generally quite thin, such as between about 1 mil and 10 mils inone embodiment. Additionally, since the polymer film can be wrappedabout the bundle 42 of optical fibers 44 and need not be extruded, thepolymer film can be wrapped directly about the optical fibers and nobarrier is required between the polymer film and the optical fiberssince the polymer film will not adhere to the tight buffer layer and/oroptical fiber in the same manner that an extruded polymeric jacket wouldadhere to the tight buffer layer of the tight buffered optical fibers ofa conventional unitized fiber optic cable. Although the polymer film canbe formed of various materials, the polymer film of one embodiment isformed of polyester, such as a polyethylene terephthalate, having athickness of about 1 mil. For example, the polymer film may be a MYLAR®film having indicia, for example, different colors to identify differentbundles 42. Additionally, bundle 42 may also be disposed within a softhousing such as disclosed in U.S. patent application Ser. No. 09/966,646filed on Sep. 28, 2001, which is incorporated herein by reference.

Cable jacket 50 can be formed of various materials, but is typicallyformed of a plastic, such as PVC. As an alternative to the PVC, cablejacket 50 may be formed of other plastics including fiber-reinforcedpolyethylene, a fluoro-plastic, such as PVDF, a fluoro-compound asdisclosed by U.S. Pat. No. 4,963,609, blends of PVC and PVDF, blends ofPVC and PE, or other suitable polymeric blends. As described above inconjunction with the tight buffer layer of the tight buffered opticalfibers 44, cable jacket 50 can also be designed to have increased flameresistance such that the fiber optic cable has a riser, a plenum and/ora low smoke zero halogen rating. In this regard, cable jacket 50 caninclude aluminum trihydrate, antimony trioxide or other additives thatincrease the flame resistance of the cable jacket as known to thoseskilled in the art and as described by U.S. Pat. No. 6,167,178.Additionally, cable jacket 50 can be designed to be resistant to UVlight, if so desired.

Cable jacket 50 is typically extruded about the plurality of bundles 42of optical fibers 44. Since bundles 42 of optical fibers 44 need not bejacketed as described below, fiber optic cable 40 preferably includes aseparation element and/or layer 52 (FIG. 4) for inhibiting adhesionbetween the plurality of bundles of optical fibers and cable jacket 50.Separation element 52 includes a separation layer disposed within cablejacket 50 and surrounding the plurality of bundles 42 of optical fibers44. Separation layer 52 is preferably formed of a material having amelting point that is greater than the respective melting point(s) ofcable jacket 50 and, if used, the tight buffer layer of the tightbuffered optical fibers 44 in order to inhibit adherence between cablejacket 50 and the bundles of optical fibers. For a cable jacket 50formed of PVC having a melting temperature of 190° C., separationelement 52 can be formed of a polyester, such as a MYLAR® film having amelting point of about 235° C.

Cable jacket 50 is typically extruded about the plurality of bundles 42of optical fibers 44 at the melting temperature of the plastic thatforms the cable jacket. By being formed of a material, such as apolyester, having a melting point greater than the melting point of theplastic that forms cable jacket 50, separation layer 52 does not melt ascable jacket 50 is extruded thereover. As such, separation layer 52inhibits adherence between cable jacket 50 and the bundles 42 of opticalfibers 44 such that the optical fibers are able to move somewhatrelative to cable jacket 50 as fiber optic cable 10 is flexed or bent,thereby permitting optical signals to be transmitted via the opticalfibers without disadvantageous optical attenuation as fiber optic cable10 is bent or flexed.

As shown in FIG. 2, strength members 46, for example an aramid yarn suchas Kevlar®, at least partially performs as separation layer 52 whileproviding tensile strength to fiber optic cable 40. However, othersuitable strength members 46 may be used, for example, Zylon®, Vectran®,Technora®, or Spectra®. Strength members 46 may have a paralleldirection of lay relative to bundles 42 of optical fibers 44 or may bestranded about bundles 42. However, in order to reduce the quantity ofaramid yarns used for coverage, rather than strength, separation layer52 can be formed of various other tapes, films, threads and/or fibrousmaterials. For example, separation layer 52 can be formed from aplurality of Kevlar® ends and a plurality of polyester yarn endsstranded around a bundle 44. In each of these embodiments, however,separation layer 52 is designed to inhibit adhesion between theplurality of bundles 42 of optical fibers 44 and cable jacket 50.Moreover, separation layer 52 of each of these embodiments is generallyrelatively thin so as not to unnecessarily increase the size of fiberoptic cable 40.

Separation layer 52 can be formed of other, non-polymeric materials, ifso desired. For example, separation layer 52 can be formed of a waterswellable tape in order to increase the water resistance of fiber opticcable 40. Additionally, a separation layer 52 may be formed of a MYLAR®film having a thickness of about 1 mil.

Separation element 52 can be formed in other manners without departingfrom the spirit and scope of the present invention. For example, in theembodiment of fiber optic cable 40 depicted in FIG. 4, each bundle 42 ofoptical fibers 44 includes a polymer film 48 surrounding the pluralityof tight buffered optical fibers 44; however, optical fibers 44 may benon-tight buffered. By appropriately designing polymer film 48, polymerfilm 48 not only serves as the binder for the respective bundle 42 ofoptical fibers 44, but also serves as the separation element. In thisregard, polymer film 48 is preferably formed of a material having amelting point greater than the melting point of the plastic that formscable jacket 50. For example, for a fiber optic cable 40 having a cablejacket 50 formed of PVC having a melting point of 190° C., polymer film48 can be formed of a polyester, such as a MYLAR® film, having a meltingpoint of 235° C. As such, the polymer film 48 surrounding each bundle 42of optical fibers 44 will not melt as cable jacket 50 is extruded aboutthe plurality of bundles of optical fibers. Thus, polymer film 48 willserve to inhibit adhesion between cable jacket 50 and the plurality oftight buffered optical fibers 44 of each bundle 42.

Still further, separation element 52 can be formed of a surface coatingon each bundle 42 of optical fibers 44. In this regard, the surfacecoating is preferably applied to at least that portion of each bundle 42of optical fibers 44 that would otherwise contact cable jacket 50. Thesurface coating is preferably formed of a material that also has amelting point greater than the melting point of the plastic from whichcable jacket 50 is formed. For example, the surface coating may beformed of powdered talc that is applied to the outer surface of theplurality of bundles 42 of optical fibers 44. The surface coating oftalc effectively inhibits adhesion between cable jacket 50 and the tightbuffered optical fibers 44 as the cable jacket is extruded thereover.

According to one embodiment of the present invention, each individualbundle 42 of optical fibers 44 is unjacketed. That is, each individualbundle 42 of optical fibers 44 is bound together by a binder element 48,such as a binder thread, a thin polymeric layer or the like, and doesnot include a polymeric jacket as in conventional unitized fiber opticcables. As such, those embodiments of fiber optic cable 40 in which eachbundle 42 is bound with a binder thread 48 permit direct contact betweenthe non-tight buffered optical fibers and/or tight buffered opticalfibers of adjacent bundles.

The jackets surrounding the bundles of optical fibers of conventionalunitized fiber optic cables are relatively thick. Likewise, the layer ofstrength members, tight buffering, or the like disposed between thejacket of each individual bundle of optical fibers and the opticalfibers is also relatively thick. By designing fiber optic cable 40 suchthat the bundles 42 of optical fibers 44 need not include a polymericjacket and/or a layer of strength members for separating the opticalfibers from the polymeric jacket, each bundle of optical fibers can besubstantially reduced in size and, correspondingly, fiber optic cable 40can be substantially reduced in size. Likewise, non-tight bufferedoptical fibers 44 can substantially reduce bundle size and,correspondingly, fiber optic cable 40 can be substantially reduced insize.

For comparison purposes, fiber optic cable 40 according to oneembodiment of the present invention has six bundles 42 of optical fibers44 with each bundle of optical fibers including six tight bufferedoptical fibers stranded about a central strength member 46. While thesize and thickness of various cable components may be varied dependingupon the application, such as by varying the thickness of cable jacket50 to alter the crush and impact resistance and/or the flame retardance,fiber optic cable 40 of one embodiment also includes a separation layer52 of a polyester, such as a MYLAR® film surrounding the bundles 42 ofoptical fibers 44 and a cable jacket 50 having a thickness of 1.3millimeters surrounding the separation layer such that fiber optic cable40 has a total diameter of 10.9 millimeters. As described above, aconventional unitized fiber optic cable having the same number ofbundles and the same number of total optical fibers generally has adiameter that is substantially larger, such as 18.8 millimeters. Assuch, the conventional fiber optic cable has a cross-sectional area thatis about three times larger than the fiber optic cable according to theforegoing exemplary embodiment. Thus, fiber optic cable 40 of thepresent invention can include the same number of optical fibers 44 whilebeing much smaller than conventional fiber optic cables. Alternatively,fiber optic cable 40 can include a greater number of optical fibers,i.e., a higher fiber count, while having the same size as a conventionalfiber optic cable.

While various embodiments of fiber optic cable 40 have been describedabove, fiber optic cable 40 can include other features without departingfrom the spirit and scope of the present invention. For example, fiberoptic cable 40 can be constructed to have increased water resistance byincluding a variety of water swellable tapes, threads and/or powders.For example, separation layer 52 can be formed of a water swellable tapeas described above. In another embodiment, separation layer 52 can beformed from by an armor layer, for example, a metal or dielectric layerthat may be formed from one or more pieces. In addition to acting as aseparation layer, an armor layer may provide, for example, crushresistance and/or tensile strength. In yet another embodiment, bundles42 of optical fibers 44 may be stranded around an electrical component,for example, a coaxial cable or other suitable electrical components.

While one unitized design of fiber optic cable 40 has been describedhereinabove, fiber optic cable 40 may have other configurations. In thisregard, the embodiment of fiber optic cable 40 depicted in FIG. 2includes a plurality of bundles 42 of optical fibers 44 having strengthmembers 46 and surrounded by cable jacket 50. However, in otherembodiments fiber optic cable 40 can include a number of tube assembliessurrounded by cable jacket 50 with each tube assembly including multiplebundles of optical fibers. In order to minimize the size of each tubeassembly required to contain a predetermined number of optical fibers;however, each bundle of optical fibers of a tube assembly is preferablynon-jacketed as described above in conjunction with the embodiment ofFIGS. 2 and 3.

While the bundles of optical fibers may be arranged in various manners,each tube assembly 60 of fiber optic cable 40 can include concentricbundles 42 of optical fibers 44 with some bundles of optical fiberswithin other bundles of optical fibers as depicted in the embodiment ofFIG. 5. In this regard, tube assembly 60 includes an inner bundle 42 aof optical fibers 44. Inner bundle 42 a includes a plurality of opticalfibers 44 and at least one binder thread 48 encircling the plurality ofoptical fibers to maintain the integrity of the bundle. Although notillustrated, inner bundle 42 a may also include a central strengthmember along which optical fibers 44 extend, if so desired. Inner bundle42 a can include any number of optical fibers 44, but typically includes6 or 12 optical fibers. Each optical fiber of inner bundle 42 apreferably includes indicia, such as a color, for uniquely identifyingthe respective optical fiber relative to other optical fibers of theinner bundle. While inner bundle 42 a may include various binderthreads, binder thread 48 of one advantageous embodiment is an airentangled, textured, continuous multi-filament thread as described abovein more detail.

Tube assembly 60 of the embodiment depicted in FIG. 5 also includes anouter bundle 42 b of optical fibers 44 having a plurality of opticalfibers positioned circumferentially about the inner bundle 42 a ofoptical fibers. While outer bundle 42 b may include any number ofoptical fibers, the outer bundle of the illustrated embodiment includes12 optical fibers. Like inner bundle 42 a, each optical fiber 44 ofouter bundle 42 b also preferably includes indicia, such as a color, foruniquely identifying the respective optical fiber relative to otheroptical fibers of the outer bundle. While each optical fiber 44 of innerbundle 42 a and each optical fiber of the outer bundle 42 b is uniquelyidentified, such as by having a unique color, with respect to otheroptical fibers of the respective bundle, optical fibers of inner bundle42 a may have the same colors as optical fibers of outer bundle 42 b.However, optical fibers 44 of the inner and outer bundles that have thesame color may be distinguished from one another based upon therespective bundle in which the optical fibers are included. Outer bundle42 b of optical fibers also includes at least one binder thread 48encircling the plurality of optical fibers to maintain the integrity ofthe optical fibers of the outer bundle about inner bundle 42 a. Whileinner bundle 42 a may include various binder threads, binder thread 48of one advantageous embodiment is also an air entangled, textured,continuous multi-filament thread as described above in more detail.

Additionally, tube assembly 60 of FIG. 5 can include a tubular member56, such as a buffer tube, surrounding outer bundle 42 b of opticalfibers 44 as described above. Moreover, any voids within tubular member56 may be filled with a filling compound to inhibit the migration ofwater, such as disclosed in U.S. patent application Ser. No. 09/322,625filed May 28, 1999, which is incorporated herein by reference.

As depicted in FIG. 5, at least the outer bundle 42 b of optical fibers44 and, more preferably, both the outer and inner bundles of opticalfibers are non-jacketed such that the cross-sectional size of theresulting tube assembly 60 can be minimized for a predetermined numberof optical fibers. In order to inhibit adhesion between tubular member56 and outer bundle 42 b of optical fibers 44, tube assembly 60 of FIG.5 can also include a separation element, such as a separation layer thatsurrounds the outer bundle of optical fibers or a surface coating on theouter bundle of optical fibers, as described above.

By encircling inner bundle 42 a with optical fibers 44 of outer bundle42 b, tube assembly 60 of the embodiment of FIG. 5 will include a densecollection of optical fibers in order to maximize the number of opticalfibers included within a buffer tube of a particular cross-sectionalsize. However, each optical fiber of tube assembly 60 can be uniquelyidentified by means of the indicia, such as the color, of each opticalfiber and the separation of the optical fibers into inner and outerbundles.

In one embodiment, utilizing tube assembly 60, a plurality of tubeassemblies are extended alongside a central strength member 46,typically by being stranded about central strength member 46. A cablejacket 50 is then extruded over the plurality of tube assemblies 54. Toinhibit adhesion between tubular members 56 of tube assemblies 60 andcable jacket 50, fiber optic cable 40 can also include a separationelement disposed between tube assemblies 60 and cable jacket 50 asdescribed above in conjunction with the other embodiments. By includingtube assemblies, each of which generally include multiple bundles ofoptical fibers, fiber optic cable 40 of this embodiment can include evengreater numbers of optical fibers, such as 288 optical fibers or more,while continuing to minimize the overall cross-sectional size of thecable. However, each optical fiber 44 of fiber optic cable 40 of thisembodiment may be uniquely identified since tubular member 56 of eachtube assembly 54 may include indicia, such as a color, to uniquelyidentify the respective tube assembly and the indicia, such as thecolor, of each optical fiber and the separation of the optical fibersinto inner and outer bundles permit each optical fiber of a respectivetube assembly to be uniquely identified as described above.

FIG. 6 depicts fiber optic cable 40 another embodiment of the presentinvention. Fiber optic cable 40 of FIG. 6 includes cable jacket 50 thatgenerally surrounds strength members 46 such as aramid yarns and bundle42. Bundle 42 includes a plurality of non-tight buffered optical fibers44, for example, eight optical fibers held together by binder thread 48(not shown) that inhibits non-tight buffered optical fibers 44 frombeing entangled with strength members 46. Fiber optic cable 40 of FIG. 6has a optical fiber 44 on optical fiber 44 construction among non-tightbuffered optical fibers 44; however, optical fibers 44 may include atight buffer layer. Fiber optic cable may also include a ripcord 54 forfacilitating removal of cable jacket 50. Fiber optic cable 40 of FIG. 6has a generally round cross-section and may be used as an interconnectcable.

Conventional optical fiber ribbon interconnect cables generally includea preferential bend characteristic due to the planar orientation of theoptical fibers in the optical fiber ribbon. Consequently, conventionaleight-fiber ribbon interconnect cables are difficult to bend and storein tight quarters such as splice trays. Because fiber optic cable 40 hasa generally round cross-section it generally does not have apreferential bend characteristic allowing for easier bending and routingin splice trays.

In one embodiment, fiber optic cable 40 of FIG. 6 includes a cablejacket 50 generally surrounding three ends of 2450 denier aramid yarnsstranded around a bundle 42 having eight single-mode optical fibers 44secured by binder thread 48 (not shown) with a cable diameter of about 3mm or less. However, other configurations may be used and/or the cablediameter may be greater than 3 mm. However, other suitable embodimentsmay be practiced, for example, a cable jacket 50 generally surroundingfour ends of 2450 denier aramid yarns stranded around a bundle 42 havingtwelve multi-mode optical fibers 44 secured by binder thread 48 with acable diameter of about 3–4 mm. However, the cable diameter may begreater than 3–4 mm.

FIG. 7 depicts fiber optic cable 40′ another embodiment of the presentinvention. The fiber optic cable 40′ of FIG. 7 includes a plurality offiber optic cables 40 of FIG. 6 stranded together forming a breakoutcable. Moreover, other suitable cables of the present invention may beconstructed as breakout cables. Fiber optic cables 40′ includes a firstlayer having three fiber optic cables 40 helically stranded, a secondlayer having nine fiber optic cables 40 counter-helically strandedaround the first layer, and a cable jacket 50. Embodiments of fiberoptic cable 40′ may include, for example, a separation layer 52 such asa water blocking tape, a central member, a ripcord, and/or othersuitable cable components.

FIG. 8 depicts fiber optic cable 40 another embodiment of the presentinvention. The fiber optic cable 40 of FIG. 8 includes at least oneunjacketed bundle 42 of non-tight buffered optical fibers 44 having abinding thread 48 therearound. However, optical fibers 44 may be tightbuffered and/or other binding elements may be used. Bundles 42 arestranded together; however, they may be unstranded. More particularly,fiber optic cable 40 includes a first layer having three bundles 42helically stranded and a second layer having nine bundles 42counter-helically stranded around the first layer. Separation layer 52surrounds bundles 42 of fiber optic cable 40 of FIG. 8 and is formedfrom a flexible armor. The flexible armor preferably includes a smoothinner surface for contacting bundles 42 and/or optical fibers 44. Forexample, CPID interlock armor available from Eastern Wire & Conduit ofOntario, Canada; however, other suitable armor may be used forseparation layer 52. The flexible armor may also provide bend control tofiber optic cable 40 by inhibiting small bend radii that may causeoptical attenuation. A cable jacket 50 surrounds the armor separationlayer 52 of FIG. 8; however, embodiments of FIG. 8 may be practicedwithout cable jacket 50.

Additionally, fiber optic cable 40 of FIG. 8 does not include a bundleand/or a cable jacket within separation layer 52; however, embodimentsmay be practiced with bundle jackets. Eliminating a jacket fromindividual bundles 42 and/or a jacket around the stranded bundles 42within the armor separation layer 52 allows for a higher optical fiberpacking density within the armor separation layer 52. Embodiments offiber optic cable 40 of FIG. 8 may include, for example, a centralmember, a ripcord, a water blocking tape wrapped around the bundlesand/or other suitable cable components.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A fiber optic breakout cable comprising a plurality of cable unitsdisposed within an outer jacket, wherein each of the plurality of cableunits comprises: at least one bundle, the at least one bundle comprisinga plurality of non-tight buffered optical fibers and a binder elementfor maintaining the plurality of non-tight buffered optical fibers inthe at least one bundle; a separation layer contacting at least some ofthe plurality of non-tight buffered optical fibers, wherein theseparation layer is formed from a plurality of tensile yarns forproviding a tensile strength characteristic for the cable unit; and acable unit jacket, the cable unit jacket surrounding the at least onebundle and the separation layer and contacting a portion of theseparation layer thereby forming the respective cable unit, wherein theseparation layer inhibits adhesion between the at least one bundle andthe cable unit jacket and wherein the fiber optic breakout cableexcludes a grease or a gel composition being in contact with the atleast one bundle for filling interstices of the cable unit therebyblocking water from flowing through the cable.
 2. The fiber opticbreakout cable of claim 1, wherein the plurality of cable units eachhave twelve optical fibers.
 3. The fiber optic breakout cable of claim1, wherein the plurality of cable units have a diameter of about 4millimeters or less.
 4. The fiber optic breakout cable of claim 1, thebinder element being selected from a binder thread, a binder yarn, athin film, and a tape.
 5. The fiber optic breakout cable of claim 1, thebinder element being a binder thread encirling the plurality ofnon-tight buffered optical fibers.
 6. The fiber optic breakout cable ofclaim 1, the plurality of cable units being stranded around a centralmember.
 7. The fiber optic breakout cable of claim 1, further includingan armor layer.
 8. The fiber optic breakout cable of claim 1, furtherincluding a plurality of strength members disposed between the outerjacket and the respective cable unit jackets of the plurality of cableunits.
 9. The fiber optic breakout cable of claim 1, the cable unitjacket contacting at least a portion of the separation layer being aninner surface of the cable unit jacket.
 10. A fiber optic breakout cablecomprising two cable units disposed within an outer jacket, wherein oneof the cable units comprises: at least one bundle, the at least onebundle comprising a plurality of non-tight buffered optical fibers and abinder element for maintaining the plurality of non-tight bufferedoptical fibers in the at least one bundle; a separation layer, theseparation layer being adjacent to at least some of the plurality ofnon-tight buffered optical fibers, wherein the separation layer isformed from a plurality of tensile yarns for providing a tensilestrength characteristic for the cable unit; and a cable unit jacket, thecable unit jacket surrounding the at least one bundle and the separationlayer and having a diameter of about 4 millimeters or less, wherein thecable unit jacket contacts a portion of the separation layer, whereinthe separation layer inhibits adhesion between the at least one bundleand the cable unit jacket and wherein the fiber optic breakout cableexcludes a grease or a gel composition being in contact with the atleast one bundle for filling interstices of the cable unit therebyblocking water from flowing through the cable.
 11. The fiber opticbreakout cable of claim 10, wherein the plurality of cable units eachhave twelve optical fibers.
 12. The fiber optic breakout cable of claim10, the binder element being selected from a binder thread, a binderyarn, a thin film, and a tape.
 13. The fiber optic breakout cable ofclaim 10, the binder element being a binder thread encirling theplurality of non-tight buffered optical fibers.
 14. The fiber opticbreakout cable of claim 10, further including an armor layer.
 15. Thefiber optic breakout cable of claim 10, further including a plurality ofstrength members disposed between the outer jacket and the cable unitjacket of the one cable unit.
 16. The fiber optic breakout cable ofclaim 10, the plurality of non-tight buffered optical fibers furtherincluding a tight buffered layer.
 17. The fiber optic breakout cable ofclaim 10, the cable unit jacket that contacts the a portion of theseparation layer being an inner surface of the cable unit jacket.
 18. Afiber optic cable comprising: at least one bundle, the at least onebundle comprising twelve non-tight buffered optical fibers and a binderelement for maintaining the non-tight buffered optical fibers in the atleast one bundle; a separation layer contacting at least one of thetwelve non-tight buffered optical fibers, wherein the separation layeris formed from a plurality of tensile yarns for providing a tensilestrength characteristic; and a cable jacket, the cable jacket contactinga portion of the separation layer, wherein the separation layer inhibitsadhesion between the at least one bundle and the cable jacket andwherein the fiber optic cable excluding a grease or a gel compositionbeing in contact with the at least one bundle for filling interstices ofthe cable jacket thereby blocking water from flowing through the cable.19. The fiber optic cable of claim 18, wherein the fiber optic cable hasa diameter of about 5 millimeters or less.
 20. The fiber optic cable ofclaim 18, the binder element being selected from a binder thread, abinder yarn, a thin film, and a tape.
 21. The fiber optic cable of claim18, the binder element being a binder thread encirling the plurality ofnon-tight buffered optical fibers.
 22. The fiber optic cable of claim18, the cable jacket contacting a portion of the separation layer beingan inner surface of the cable jacket.